Abundance of Juvenile Shrimp 



Kenneth N. Baxter 



To obtain a possible index of later abundance of adult shrimp, the 

 monitoring of the passage of postlarval shrimp into Galveston Bay was begun 

 November 1959- Samples are taken semiweekly using a hand-drawn, beam 

 trawl fitted with a plankton net in the cod end. A station was established in- 

 side the entrance to Bolivar Roads near the south jetty on the sand flats (SF 

 on figure). Samples were taken at this station from November 1959 to May 

 1961 and from August 11. 1961. until September 8, when flood waters from 

 Hurricane Carla cut a channel 200 feet wide and 14 feet deep through the sand 

 flats adjacent to the jetty, making the station site inaccessible. A new mon- 

 itoring station was then located on Bolivar Peninsula in a cove off State High- 

 way 87 opposite the abandoned lighthouse (BSF on figure). This station was 

 occupied from September 25 to November 21 of 1961. when a third station site 

 was selected on the beach, midway between the north jetty and the Fort Travis 

 ruins on Bolivar Peninsula (NJSF-1 on figure), where twice weekly sampling 



is currently being carried on. , . ^ , 



The sample is taken 



in the following manner. A stake 

 is driven into the ground at the 

 shoreline. A 150 -foot nylon 

 cord is attached to the stake arfd 

 stretched taut parallel to the 

 waterline. Using the cord as 

 a constant radius., the operator 

 pulls the net assembly along the 

 bottom in a half circle. The ef- 

 fective length of the tow is 426 

 feet, the volume of water sam- 

 pled is 2.477 cubic feet, and the 

 area of bottom traversed is 

 1,958 square feet. These are 

 average measurements and vary 

 according to the shoreline 's 

 configuration. 



Through the winter 

 months, great variations in num- 

 bers of postlarvae between sam- 

 pling periods appeared to be re- 

 lated to fluctuations in tempera- 

 ture. Follovsring rapid drops in 

 temperature, very few postlarvae were coUected. and on several occasions 

 numbers of dead postlarval penaeids were noted. For instance, on March 1, 

 1962, about 75 dead postlarvae were found in the sample. This was after a 



Postlarval sampling stations at the 

 entrance to Galveston Bay. 



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